Exemplary embodiments of the present invention relate to a technology for fabricating a semiconductor device, and more particularly, to a method for forming contact holes of a semiconductor device.
Pattern shrinkage occupies a core factor for increasing production yield in the development of a semiconductor device. According to the pattern shrinkage, a process of forming a contact hole in a semiconductor device using under 30 nm process is regarded as one of the difficult processes.
Therefore, there are demands for the development of a patterning technology for forming a contact hole having a diameter and space using under 30 nm design rules. To this end, a double patterning technology (DPT) is introduced.
FIGS. 1A to 1E are perspective views illustrating a conventional method for forming contact holes in a semiconductor device, and FIG. 2 is a plan view illustrating contact holes of a semiconductor device fabricated according to conventional technology.
Referring to FIG. 1A, an etch target layer 12, a first hard mask layer 13, and a second hard mask layer 14 are sequentially formed over a substrate 11 where certain structures are formed. Here, to secure the etch selectivity between the first hard mask layer 13 and the second hard mask layer 14, the first hard mask layer 13 and the second hard mask layer 14 may be formed of heterogeneous materials. For example, the first hard mask layer 13 may be formed of an organic material, such as an amorphous carbon layer (ACL), and the second hard mask layer 14 may be formed of an inorganic material, such as an oxide layer.
Subsequently, a first photoresist layer pattern 15 is formed over the second hard mask layer 14. The first photoresist layer pattern 15 is a line/space type, and the ratio of lines (L) to spaces (S) of the first photoresist layer pattern 15 is 1:1.
Referring to FIG. 1B, the second hard mask layer 14 is etched using the first photoresist layer pattern 15 as an etch barrier so as to form a first hard mask pattern 14A which is a line/space type stretched in a first direction.
Subsequently, the first photoresist layer pattern 15 is removed.
Referring to FIG. 1C, a second photoresist layer pattern 16 of a line/space type stretched in a second direction perpendicular to the first direction is formed over the substrate structure including the first hard mask pattern 14A. Here, the ratios of lines (L) to spaces (S) of the first photoresist layer pattern 15 and the second photoresist layer pattern 16 are the same.
Referring to FIGS. 1D and 1E, the first hard mask layer 13 is etched using the first hard mask pattern 14A and the second photoresist layer pattern 16 as etch barriers so as to form a second hard mask pattern 13A. As a result, an opening portion 17 defining an area of a contact hole is formed in a region where the first hard mask pattern 14A and the second hard mask pattern 13A do not cover.
Subsequently, after the second photoresist layer pattern 16 is removed, the etch target layer 12 is etched using the first hard mask pattern 14A and the second hard mask pattern 13A as etch barriers so as to form a plurality of contact holes 18.
Subsequently, when the first hard mask pattern 14A and the second hard mask pattern 13A are removed, it can be seen that the plurality of the contact holes 18 are formed in the etch target layer 12 (see FIGS. 1E and 2).
As the dotted line of FIG. 2 shows, the contact holes 18 are to have a symmetric circular shape, and the spaces between adjacent contact holes 18 in the first and second directions are to be uniform.
According to the conventional technology, however, since the first hard mask layer 13 and the second hard mask layer 14 are formed of heterogeneous materials, there is a concern in that the contact holes 18 are formed asymmetrically. Also, since the contact holes 18 are formed in an asymmetric shape, the space between adjacent contact holes 18 in the first and second directions are not uniform. This is because the etch characteristics of the organic material and the inorganic material are different from each other. Although the first photoresist layer pattern 15 and the second photoresist layer pattern 16 are formed to have the same ratio of lines (L) to spaces (S), the first hard mask pattern 14A and the second hard mask pattern 13A that are formed using the first photoresist layer pattern 15 and the second photoresist layer pattern 16 as the etch barriers may not have the same ratio of lines (L) to spaces (S).
Also, since the first hard mask layer 13 and the second hard mask layer 14 are formed of the heterogeneous materials, different etch conditions, such as etch equipment, etch method, and etchant gas, are to be applied to form the first hard mask pattern 14A and the second hard mask pattern 13A. Therefore, the process becomes complicated and yield is deteriorated.
In addition, since the semiconductor device is formed based on inorganic materials, the first hard mask layer 13 which is formed of an organic material has poor adhesion to the inorganic materials. Therefore, an adhesive layer (not shown) is formed in the upper and lower portions of the first hard mask layer 13. Moreover, since the organic material has inferior etch resistance to the inorganic materials, an auxiliary layer (not shown) is to be formed as well to supplement the etch resistance of the first hard mask layer 13. As a result, since the overall thickness (or height) of the hard mask layer is increased, the asymmetrical formation of the contact holes 18 may become more significant and the process may become more complicated.
Also, the organic material is likely to be deformed or lost at a high temperature, the second hard mask layer 14 formed over the first hard mask layer 13 is to be formed of an inorganic material that may be formed at a low temperature. Therefore, there is limitation in selecting an inorganic material usable for the formation of the second hard mask layer 14.